Certain vehicle systems include the transport of liquid droplets within a flow of gas, such as in a vehicle exhaust treatment system or an engine fuel intake system. Controlled dispersion of the liquid droplets within the flow may be advantageous for several reasons. For example, in one type of vehicle exhaust system, liquid hydrocarbons (HC) are injected within a gas flow to a diesel oxidation catalyst (DOC) that is upstream of a diesel particulate filter (DPF). The hydrocarbon is oxidized in the DOC in an exothermic reaction, creating the high temperatures necessary in the downstream DPF for burning diesel particulate, thus burning off the particulate to regenerate the DPF and reduce system backpressure. In another example, a diesel exhaust fluid, such as urea or another liquid reductant of oxides of nitrogen (NOx), is injected upstream of a catalyst, such as a selective catalyst reduction (SCR) catalyst, where it is converted to ammonia that is used to reduce Nox to nitrogen (N2). In another example, hydrocarbons are periodically injected into the exhaust flow upstream of a lean Nox trap to regenerate the trap. In an engine fuel intake system as well, liquid fuel is entrained in air flow for combustion in the engine cylinders.